In recent years the emissions from external and internal combustion engines, mainly carbon monoxide, hydrocarbons and nitrogen oxides, have been receiving serious social attention as the major source of air pollution. Various methods have been studied industrially to control the generation of these harmful gases and different devices for the practical application of these methods have been developed.
Various measures are being taken, such as Electronic Fuel Injection, in which a sensor mounted on a vehicle detects its running condition, which is assessed by a computer; Exhaust Gas Recirculation systems, in which the exhaust gas is recirculated into the suction system; or Air Injection, in which the air sucked into the air-cleaner by the air pump is controlled by a bypass valve and ejected to the rear of the exhaust valve. These measures, however, cannot be called perfect; they are nothing more than temporary stopgaps.
Meanwhile, in an effort to abate harmful auto emissions, use of natural gas as a secondary fuel to the vehicle is being tried, but only with limited success.
For instance, as R.W. Mcjone and R.J. Corbel report in an SAE paper No. 700078 (published 1971), gasoline-burning vehicles have been equipped with a fuel-exchanger, by which the gasoline and the natural gas are initially used in combination, and the fuel supply is switched to natural gas alone when a steady running state is established. At the present stage, however, this approach requires large tanks for the transportation of the materials; a tremendous investment has to be made for the installation of storage facilities; and the running range of such vehicles is limited on account of the oil supply thereto.
According to the SAE Paper No. 720670 written by Marc S. New Kivk, International Materials has developed a Boston Fuel-Reforming Car, in which carbon is precipitated within a reactor by cracking of hydrocarbons under high-temperature and high-pressure conditions without any catalyzer, and the carbon monoxide and steam generated by the reaction with steam are turned into hydrogen and carbonic gas. As the reaction has to take place at temperatures higher than 950.degree.C and at a reactor pressure of 55.8 kg/cm.sup.2, this method requires materials which can stand high temperature and high pressure; and as the generated hydrogen fuel has to be burned to heat up the reactor, much money is needed for fuel. Since it involves the generation of carbon monoxide, this method involves the risk that this harmful gas will leak out in the event of an accident. A reservoir for the generated gas has to be provided and accordingly the vehicle might as well be equipped with a hydrogen cylinder, which poses an exceedingly high hazard. Since such a cylinder is of the high pressure type, naturally the pump for supplying the material has to be a high pressure pump, which inevitably increases the cost.